In the field of power electronics and control, the user of space vector pulse width modulation (PWM) techniques to control the generation and delivery of three phase voltage output from a direct voltage (DC) power source has been known. In such systems, the output signal can be, or can approximate, an alternating voltage and/or alternating current (AC) signal having three independent phases separated by one hundred twenty degrees. The three signals produced by such known space vector PWM platforms can be used to drive the inductors or other components of a motor or other output load. The use of space vector PWM techniques has permitted the control of three phase voltage to motors and other loads using relatively flexible and inexpensive programmed electronic control modules. In space vector PWM platforms, a set of space vectors, encoded as three-bit values, can be used to drive or control a set of three phase switches whose switching action can produce voltage levels that approximate an alternating voltage output in the three component phases. Voltage regulation for the management of power supplies in large home or other hardware, such as the electric motors used in heat pump, air conditioning, and other heating and cooling systems has been accomplished using space vector PWM controllers for some commercially available systems. Besides lower cost, such systems can also permit an enhanced degree of programmability in voltage, net power, and/or other parameters of the power supply platform and its output.
In the field of power electronics and other applications, it has likewise been known to use a type of power generation circuitry referred to as “bootstrap” capacitor or charging circuits. In bootstrap capacitor circuits, a set of capacitors can be coupled across different signal paths in electrical supply circuits, to parasitically tap the current in those circuits that flows during other operations. The bootstrap capacitor or capacitors build up charge as a result, and that stored charge can be used later to supply power to other circuits, and/or for other purposes. In cases, depending on load demands, the power delivered by a set of bootstrap capacitors can be used as a substitute for traditional transformers or other power supply elements. When bootstrap capacitor circuits are successfully used as a substitute for transformers or other power supply elements, significant cost savings can be achieved.
In the case of space vector PWM platforms, bootstrap capacitor power circuits could, potentially, form a useful alternative to transformer-based alternating voltage and/or alternating current (AC) power supplies, which tend to use large and expensive coil windings and other parts. In such a scenario, a set of bootstrap capacitors could potentially be inserted in the three phase switching circuitry, and draw current from that circuitry for storage and use when generating the inverted AC voltage output to drive the load.
Implementations to incorporate bootstrap capacitor circuitry in five-segment space vector PWM systems in which the PWM signals that drive the set of phase switches are reduced from a total of six clock cycles per segment (corresponding to one cycle per switch), to five clock cycles per segment to reduce the number of PWM state transitions and switching loss have, however, failed to materialize or become known in existing platforms. This may be due, in part, to the requirement in bootstrap capacitor circuitry that the signals from which each bootstrap capacitor draws current be in an “on” or flowing state for long enough to charge that capacitor by the time it is called upon to discharge and deliver power. In known five-segment space vector PWM systems, the rapid switching between off and on states in the set of (three) phase switches based on the cycling of conventional space vector sequences prevents any bootstrap capacitor from achieving a fully pre-charged state by the time that capacitor would be next called upon to discharge and deliver power.
It may be desirable to provide methods and systems for space vector pulse width modulation switching using bootstrap charging circuits, in which space vector PWM systems can be configured with bootstrap capacitor power circuitry, yet still provide the constituent capacitors adequate time to achieve the necessary level of charge to produce full three-phase output.